This invention relates to an apparatus for determining the amount and location of unbalance in rotating vehicle wheels, and more particularly to a balancing apparatus of the type whereon such wheels can be balanced without removing them from the vehicle.
It is currently known to balance a road vehicle wheel by using two different types of apparata. With one apparatus, the wheel is balanced separately from the vehicle proper, whereas with the other apparatus the wheel is balanced while mounted to the vehicle at its natural operative location. Since, with the latter type of apparatus, the wheels are balanced at their natural location and in a nearly actual operation condition, such an apparatus is to be considered more accurate. Indeed, since on the former type of apparatus the wheels are balanced after removal from the vehicle, on re-installing them on the vehicle, owing to the gravitational force, they take up a different mounting position with respect to the rotation center when they were pivoted on the balancing apparatus, this new position causing unbalance. Furthermore, those parts which rotate together with the wheels are not balanced, and this further aggravates the unbalance situation. In spite of their balancing inaccuracy, those apparata which balance removed wheels are still widespread and currently marketed on account of the fact that those apparata which balance wheels in their mounted condition are difficult to use and time consuming. Thus, the need is felt in this field for a mounted wheel balancing machine which, while retaining the accuracy feature mentioned above, is capable of eliminating those operational difficulties to make the balancing step a simple and straightforward one, without requiring a qualified operator, and this at reduced operation times.
The apparata for balancing wheels while mounted to a road vehicle, although differring somewhat in design, are all based on the same principle, and the balancing operation is basically the same: the wheel to be balanced is lifted off the ground or floor by means of a jack placed under the vehicle, and an indexing mark is applied, with a piece of chalk or adhesive tape, to any point of the tire outer flank, such index being often taken to be the inflation valve itself. A pulse detector or pick-up is then placed under the vehicle as near as possible to the wheel to be balanced; some detectors have one end resting on the ground or floor surface and the other contacting the vehicle, others do not rest on the ground or floor but remain attached to the vehicle through the action of a magnet, and others still are incorporated in the jack itself. The detector is connected to the balancing machine, comprising generally an unbalance indicating gauge and a stroboscopic lamp, and the wheel to be balanced, when an idle one, is caused to rotate by means of a pulley drive, and when a drive one, by means of the vehicle own engine. If the wheel is out of balance, the detector beneath the vehicle receives a blow at each revolution when the unbalanced portion, and accordingly heavier portion, is at its lowest point, that blow, after being converted into an electric pulse, being transferred to the stroboscopic lamp and gauge; the former lights up and, by the stroboscopic effect, shows the wheel as if it were stationary, and the latter indicates the amount of unbalance which varies according to the wheel rotational speed; the position of the indexing mark applied to the wheel is then observed at the precise moment that the gauge shows maximum unbalance. After such readings have been taken, the wheel is stopped and the indexing mark applied to the wheel is moved to the location whereat it was observed at the moment of maximum unbalance, while to the topmost or 12 o'clock portion of the wheel a counterweight is applied in the amount indicated by the gauge. It will be apparent that with this balancing method it is necessary to take simultaneously two different readings which are away from each other and moving, since both the gauge pointer and the wheel mark vary simultaneously as the speed varies.
It is this necessity of observing two points away from each other that makes the balancing operation a difficult one. In the case of the drive wheels, an additional drawback resides in the fact that an assistant has to be available for starting the vehicle engine and throttle up or down as necessary while the ground operator reads the gauge and mark on the wheel.